Reinforced grinding wheel and reinforcing structure therefor



m 25, W57 J. T. ZAWODNI ETAL 3,315,418

REINFORCED GRINDING WHEEL AND REINFORCING STRUCTURE THEREFOR Filed Sept.14, 1964 v INVENTORS b q JAMES T. ZAWODNI L j ROBERTJ. MARKOTANATTORNEYS United States Patent 3,315,418 REINFORCED GRINDING WHEEL ANDREIN- FORCIN G STRUCTURE THEREFOR James T. Zawodni, Birmingham, andRobert J. Markotan,

Allen Park, Mich, assignors to Acme Abrasive Co.,

Warren, Mich, a corporation of Michigan Filed Sept. 14, 1964, Ser. No.396,113 4 Claims. (Cl. 51-206) The present invention relates toimprovements in a revinforced grinding or abrasive wheel, in particularsuch as the snagging wheels widely used in the steel foundry and relatedindustries where a high rate of metal removal is desired, although othertypes of abrasive wheel are contemplated. The invention also relates toa novel reinforcing structure or component of such wheel, rendering thelatter proof against the all-too-well known danger of bursting as theresult of abuse. This hazard attends the development of a crack orcracks extending radially outwardly from the inner periphery of thewheel, and it is necessary to discard the wheel upon discovery of thedamage.

Many efforts have been made to meet the problem of wheel cracking anddisintegrating by internally reinforcing the granular abrasive structureof the wheel. Metal reinforcing components of ring-like or other naturehave been embedded in the wheel body; but they must be positionedrelatively closely adjacent the inner periphery of the wheel in order topreserve some practical measure of effective life of the latter beforethe metal is exposed; and the likelihood of developing dangerous wheelcracks outwardly thereof still exists. Likewise, non-metallic fabricmaterials have been incorporated in the wheel body, as in layers,chopped or chunk fabric disposed therein in a random or ordered fashion,cord materials, and the like. However, for one reason or another littlesuccess has accompanied these efforts, particularly in respect to largerdiameter snagging wheels.

More recently it has been proposed to employ fiberglass cloth or cordingembedded in the abrasive mass of the wheel for the purpose, as in theform of rings coaxial with the wheel axis or fiberglass cords arrangedin one special pattern or another in relation to the axis. However,considerations of cost or other considerations have obstructed theseexpedients. Particularly in instances in which fiberglass strand or cordmaterial is embedded in the wheel in a special outline intended tocombat the radial stress factor, objections arise which it is the objectof the present invention to eliminate.

That is, when the glass fiber reinforcing material takes the form of acoaxial ring, the progression of wear on the wheel at high snaggingspeed soon exposes the reinforcing annulus about its entire periphery,thereby materially diminishing the effectiveness of the wheel. On theother hand, when the fiberglass cord is built in the Wheel in a special,non-circular pattern, the overlap of cord lengths upon one another underquite heavy axial compression in the molding procedure causes the cordmaterial at overlap zones to be strongly compressed. Then, upon releaseof pressure on the molded wheel, the cords tend to spring apart, therebysetting up an internal, axially directed stress in the wheel tode-laminate the latter. This introduces a further weakening effect, overand above the stress which the reinforcement is intended to combat.

Therefore, the present invention provides an internal reinforcingstructure of an improved sort for an abrasive wheel, and a wheelreinforced strongly by such component, in which the reinforcement takesthe form of elongated fiberglass cord material, preferably a singlecord, which is spirally arranged in a single plane, with theconvolutions thereof substantially and preferably uniformly, spacedradially from one another in progression from the inner diameter to theouter periphery of the wheel.

The cord is composed of a plurality of slightly or loosely twistedstrands and the strands are each in turn composed of a multiplicity offiberglass filaments or so-called ends.

The invention is based on the concept that the most important of thestresses to be resisted in the reinforcing of an abrasive wheel againstbursting is a tangential one, not radial.

Thus, in the case of glass fiber cord material laid out spirally and ina single plane paralleling that of the wheel and within its axialconfines, the successive convolutions of the cord, in progressionradially outwardly thereof, present successive barriers at which theinternal stress apt to occasion radial outward cracking of the granularmass, thus initiating the tangential forces, is at once opposed andblocked by the reinforcing cord in tension.

In this type of uni-planar, spirally developing layout of cord material,only a single tail end of the cord will be exposed under wheel wear atany given moment, so that the reduction of grinding area isinsignificant, as compared, for example, with that of a ring-reinforcedwheel, or a wheel reinforced by cord material having a large number ofradially extending components.

Further in accordance with the invention, the filaments or ends of fiberglass of component strands and the ends themselves, are impregnated in aresinous mate-rial compatible with the resin binder of the abrasivewheel body in which the reinforcing structure is embedded.

Another object of the invention is to provide an abrasive wheel having areinforcing structure of the type described, in which the strands of thespiral reinforcing material are twisted, or otherwise conformed, onlyslightly or slackly, and, as bonded by the resinous material referredto, remain subtsantially linear and parallel parts of the cord. Thereason for this is that an excessive twisting or braiding of the strandcomponents (heretofore alleged to increase the bonding interlock of thestrand with the abrasive and bonding material) has been found by usactually to cause the braided or twisted elements to exert a cutting andweakening action on one another, both under axial compression andcircumferential tension.

In further accordance with the invention, a single spiral reinforcingmember of the character described may be incorporated in the wheel, or aplurality of layers of such elements, depending upon the axial thicknessof the wheel.

Moreover, the invention contemplates the provision of tie means of oneform or another acting to hold the spiral convolutions of thereinforcing structure in place prior to molding of the wheel. Such tiemeans may take the form of a length or lengths of material (preferablythe same as that of the spiral cord) which may be fixedly associatedwith the convolutions for the desired purpose. By preference, and asshown herein, the tie means is constituted by a plurality of generallyradially extending tie elements intersecting the successiveconvolutions, and substantially coextensive in the radial direction withthe innermost and outermost convolutions.

By further preference, the tie component means in question is threadedthrough the body of successive convolutions of the reinforcement, ratherthan being laid above, below or interwoven with the convolutions. Thusthe possibility of weakening arising from the yielding and springingback of the cord material, referred to above, is minimized. However,alternative ways of fixedly associating the tie means to theconvolutions are contemplated by the invention.

In general, it is an object of the invention to provide a reinforcedabrasive wheel, and a reinforcing structure therefor, which by reason ofits spiral configuration and ready wearability, will strongly reinforcethe wheel at all of its successive convolutions under tangential stress,yet will still be exposed at only minute zones as'the abrasive masswears away. While the disclosure to follow, particularly in relation tothe specific construction of the reinforcing cord, per se, and itsperformance, is in terms of glass fiber material, it is to be understoodthat other cord materials suitable'to the purpose may be employed ashereinafter mentioned.

The foregoing as well as other objects will become more apparent as thisdescription proceeds, especially when considered in connection with theaccompanying drawing illustrating the invention, wherein:

FIG. 1 is a plan view showing the improved fiber glass reinforcingstructure of the invention as embedded in an abrasive wheel, the innerand outer peripheries of which are shown in dotted line;

FIG. 2 is a fragmentary view in section along line 22 of FIG. 1, beingsomewhat enlarged in scale;

FIG. 3 is a fragmentary view in still larger scale in section along line33 of FIG. 1;

FIG. 4 is a fragmentary perspective view illustrating a portion of atypical, lightly wound cord length of the reinforcing structure,incorporating, for example, six strands; and

FIG. 5 is a view in radial section through an abrasive wheel in which aplurality of the reinforcing structures of the invention areincorporated, this being expedient in a wheel of a greater axialthickness.

As illustrated in FIG. 1 of the drawing, the improved reinforced wheelof the invention is generally designated by the reference numeral 10,its inner diameter periphery 12 and its outer diameter periphery 14being shown in dotted line. The glass fiber reinforcing structure of thewheel is generally designated by the reference numeral 16; and itpreferably comprises a single continuous length of a suitablyimpregnated glass fiber cord material 18, of, say, three-sixteenths inchthickness. However, the thickness of gauge of the cord or cording 18 mayvary within reasonable limits. This cord is laid out in a single planein a spiral outline, successive convolutions 20 of which developoutwardly in a uniform radial spacing.

The reinforcing structure 16 further comprises a plurality (shown assix) of radially extending tie elements 22, in this case of the samematerial, spaced equally in the circumferential direction from oneanother, and of respective radial lengths such as to only slightlyradially over-extend the innermost and outermost convolutions 20 of thestrand series which they tie together stably. As indicated above,however, other types of cord tie-in arrangement may be utilized.

Physical and dimensional relationships of the wheel 10 and itsreinforcing structure 16 will be hereinafter described in furtherdetail; and while FIGS. 1-3 and 5 of the drawing (in particular FIGS. 2and 5) schematically and for convenience show the cord 18 as being trulycircular in cross-section, this, of course, cannot actually be the casein any cord which is a twisted one. The shape is depicted moreaccurately in FIG. 4. Furthermore, the mentioned dimensional factors aresubject to change within reasonable limits.

In connection with FIG. 4, the cord 18 is shown as being composedtypically of six strands 24 which are twisted only enough to hold thesame stably together, as impregnated and thus loosely formed; so thatthe effect is one of substantially linear, parallel and longitudinalcord components. For example, the degree of twist may be only such as toimpart a full 360 helical pitchrfor each 4 /2"-5 of length of the cord18. The invention is not unduly limited, however, in this respect, butthe fact remains that the absence of a tightly twisted or braidedformation eliminates a cause of inter-cutting of the strand filamentsand ends under tension and axial compression, and does not significantlydecrease the strength of the cord 18.

As those skilled in the art will readily appreciate, the

. 4 composition of the abrasive body of the wheel 10 proper may varyconsiderably, and such variations (consistent with the primary intendedpurpose for use in a grinding wheel) are of course contemplated by theinvention.

Typically, however, the abrasive mass will have an approximatecomposition, by volume, as follows: (a) aluminum oxide, silicon carbideor other abrasive grit, 56%; (b) a suitable bonding agent (includingfiller), such as a powdered, phenolic, epoxy or other bonding agentavailable to those skilled in the art, 24%; and (c) voids or porosity,20%.

The above composition is one suitable for the production of a wheelunder a conventional cold press molding procedure; those skilled in theart will be aware of a correspondingly effective composition for use inthe hot press type of production. Liquids capable of use as wettingagents are furfuraldehyde, cresylic acid, furfuryl alcohol, anappropriate liquid resin, or other suitable wetting and dispersingagents known to those skilled in the art. Similarly, any appropriatefiller may be utilized. The molding of the abrasive mass, with thereinforcing structure 16 embedded therein, will be in accordance withany suitable molding procedure.

The fiber glass strand or cord material of the reinforcmg structure 16may be produced under any known specification adapted to the purpose,typical of which is a cord or plural strands of glass fiber filaments,designated as Owens Corning No. 801-F/500-60 end, impregnated in aphenolic bonding agent (or other agent compatible with the binder of theabrasive body). The above product yields a tensile strength of 270,000p.s.i. (U.S.P.). It has a normal or average resistance in tension ofabout 5.8 pounds per end, hence about 1350 pounds average for thecontemplated six strands of 60 end stock. It is content plated that thecord 18 may also aggregate 360 ends by employing but three strandcomponents, each of end rating, or any other combination may be used. Asindi cated, the above specific designation of the strand is onlyillustrative, and material of an equivalent nature is available to thoseskilled in the art. In general, we contemplate the use of a strandtotal-ling from to 480 ends or filaments.

As in the case of the abrasive mass, the twisted glass fiber cord 18 maybe produced in accordance with any known technique, with which thepresent invention is not concerned, save, as mentioned above, in regardto the degree of tightness of intertwine of its components 24.

structurally speaking, the abrasive wheel 10 shown in FIG. 1 may beinstanced, for the purpose of setting forth certain physical andpositional relationship, as being of an ID. at 12 of 12 inches, an 0.1).at 14 of 30 inches, and an axial width of three inches. In this setting,the ter'mi nus at 26 of the innermost strand convolution is locatedabout /2 inch- A inch radially outwardly of the inner wheel diameter 12,the spacing of this and successive further convolutions from one anotheris about inch, and the outermost convolution terminus at 28 is about /2inch% inch radially inward of outer wheel periphery 14. It iscontemplated that this general relationship Will obtain in the case ofwheels of greater and lesser size. Three of the reinforcing structures16 will preferably be employed in a wheel having the stated dimensions;as in the wheel, specially designated 30, in FIG. 5. In wheels ofgreater or lesser axial thickness, the number of the reinforcingstructures 16 may vary accordingly.

As arranged pursuant to FIG. 1, the several convolutions 20 are stablyheld in place by the tie elements 22. These, as spaced at equalcircumferential intervals, are positioned (FIG. 3) through the axialmidpoint of the body of the successive convolutions. While the elements22 are flattened somewhat under pressure in the molding procedure, thethreaded arrangement of the tie elements 22 very greatly minimizes acause of weakening of the wheel structure, present if the tie elementsare superposed above or below the convolutions of cord 18, or wovenacross the latter, due to the spring-back of the material upn release ofmolding pressure, setting up internal delaminating stress, as mentionedabove. However, as indicated above, the threaded relationship of tieelement to cord may be dispensed with.

It can be shown mathematically that the following tangential and radialstress factors exist in a rotating grinding wheel, if R is the wheelradius to its outer diameter, r is the radius of its hole at 12, and ris the radius at any given point within the wheel OD. and ID:

the reinforcement of an abrasive wheel and, by reasonable extension, toany analogous rapidly rotating element wherein centrifugal force is tobe resisted, whether in a material removing tool or not. Indeed, it isreasonable to expect that the adaptability of the structure 16 to suchuses will suggest to those skilled in the art others of a more or lessrelated nature. Accordingly, the claims to follow, unless otherwisespecifically limited, should be construed in the broadest senseconsistent with the state of the art of reinforcing structures.

(solid 0.1 0.2 0 3 0.4 0 0.6 0.7 0.8 wheel) Maximum Tangential StressFactor 0.98 2. 01 2. 02 2. 05 2.08 2. 13 2. 17 2. 23 2.28 lVIlXlIIllllHRadial Stress Factor 0. 96 0.81 0. 64 0.50 0. 36 0.26 0.16 0.09 0. O4 r/R 0.1 0.3 0. 4 0. 5 0. 6 0. 7 0.76 0.82 0.9

Thus, under varying values of the ratio r zR, it is seen that themaximum tangential stress factor builds up and out increasingly as thatratio increases; whereas the maximum radial stress factor diminishesoutwardly. Accordingly, the ability to withstand circumeferential ortangential stress should control in the design of a reinforcing fiberglass structure of the kind under consideration; and

it is under and in recognition of this principle that the presentinvention has evolved, as distinguished from certain heretofore proposedfiber glass reinforcing structures which emphasize the importance ofresistance to radial stress.

It is seen by reference to FIG. 1 that the outer radial termini of thetie elements 22 and the progressively receding tail 28 of the outer cordconvolution 20 have a negligible exposure, once the body of the wheelhas worn down to them.

The foregoing conclusions have been borne out by tests. In one test awheel operating at 12,500 surface feet per minute was shot, using a 30caliber rifie at a distance of about a foot and about three inches fromits hole. It was then halted and a radial crack extending from the holeto the outer periphery was observed. The wheel was run again at the samesurface speed for five minutes. No breakage occurred. This was a wheelof 24 inches by 3 inches thickness by 12 inches.

In a second test, a similar wheel was intentionally cracked across itsfull diameter. It was then run up to 18,000 surface feet per minutebefore its destroyed itself.

In a third test, another wheel dimensioned 30 X 2" x 12" was shot about3 inches from its outer periphery, while running at 12,500 s.f.p.m. Theimpact knocked a five pound segment from the outer surface of the wheel.No other disintegration occurred.

The reinforcing effect of the spiral fiber glass reinforcing structurewas proved beyond question by such tests. It can be concluded that,while, as in the case of any abrasive wheel, abuse may give rise toradially inner cracks, the convolutions 20 of the reinforcing structure16 serve as effective barriers to wheel disintegration.

As indicated above, fibers other than of glass may be utilized in themaking of the reinforcing structure 16, including its cord 18 and tieelements 22, such as asbestos fibers, snythetic fibers or blends of thesame with glass fibers and/or other fiber materials satisfactory to theobjective of the invention.

It is to be understood that in the claims to follow the expression cordis intended to signify cording or cord material in a single length or inplural lengths associated with one another in the desired spiraloutline; and that the term strand, unless so qualified, is intended todesignate a cord component 24, whether loosely twisted, as disclosed,more tightly twisted or braided, or quite unformed in any such sense,i.e., substantially rectilinear.

The foregoing description of the improved reinforcing structure 16specifically relates its use in connection with What we claim as ourinvention is:

1. A reinforcing structure, comprising glass fiber cord arranged in aspiral outline in substantially a single plane; and a plurality ofelongated, circumferentially spaced and generally radially extending tieelements holding the convolutions of the cord in their spiral outline,said tie elements being threaded through the body of successiveconvolutions.

2. A reinforcing structure, comprising glass fiber cord arranged in aspiral outline in substantially a single plane; and a plurality ofelongated circumferentially spaced and generally radially extending tieelements of material similar to said strand holding the convolutions ofthe cord in their spiral outline, said tie elements being threadedthrough the body of successive convolutions and being substantiallycoextensive radially with the respective innermost and outermostconvolutions of said cord.

3. A reinforcing structure, comprising a single length of glass fibercord arranged in a spiral outline in substantially a single plane andhaving radially progressive convolutions in substantially uniformradially spaced relation to one another, said cord comprising aplurality of elongated strands, each strand being composed of amultiplicity of glass fiber filaments, said strands being in a looselytwisted union so as to be substantially rectilinear and parallel; and aplurality of elongated, circumferentially spaced and generally radiallyextending tie elements holding the convolutions of the cord in theirspiral outline, said tie elements being threaded through the body ofsuccessive convolutions and being substantially coextensive radiallywith the respective innermost and outermost convolutions of said cord.

4. An abrasive wheel having a reinforcing structure of generally annularcharacter embedded therein generally coaxially thereof, said structurecomprising a single length of glass fiber cord arranged in a spiraloutline in substantially a single plane paralleling the sides of thewheel and having radially progressive convolutions in substantiallyuniform radial spacing relative to one another, and elongated,circumferentially spaced and radially extending tie means threadedthrough the body of successive convolutions of the cord andsubstantially coextensive radially with the respective innermost andoutermost convolutions of the cord.

References Cited by the Examiner UNITED STATES PATENTS 228,257 6/1880Hart 5l-206 1,072,532 9/1913 Turner 52-260 3,141,271 7/1964 Fischer51260 3,262,230 7/1966 Seymour 51-206 ROBERT C. RIORDON, PrimaryExaminer.

D. G. KELLY, Assistant Examiner.

4. AN ABRASIVE WHEEL HAVING A REINFORCING STRUCTURE OF GENERALLY ANNULARCHARACTER EMBEDDED THEREIN GENERALLY COAXIALLY THEREOF, SAID STRUCTURECOMPRISING A SINGLE LENGTH OF GLASS FIBER CORD ARRANGED IN A SPIRALOUTLINE IN SUBSTANTIALLY A SINGLE PLANE PARALLELING THE SIDES OF THEWHEEL AND HAVING RADIALLY PROGRESSIVE CONVOLUTIONS IN SUBSTANTIALLYUNIFORM RADIAL SPACING RELATIVE TO ONE ANOTHER, AND ELONGATED,CIRCUMFERENTIALLY SPACED AND RADIALLY EXTENDING TIE MEANS THREADEDTHROUGH THE BODY OF SUCCESSIVE CONVOLUTIONS OF THE CORD ANDSUBSTANTIALLY COEXTENSIVE RADIALLY WITH THE RESPECTIVE INNERMOST ANDOUTERMOST CONVOLUTIONS OF THE CORD.